When listening to the radio in car, with Bluetooth handsfree, the radio is interrupted when a phone call comes in but not when I play spotify or other apps (Google maps, Tunein radio or others) from Android Auto app on my Nexus 5x.
This forces me to change the car radio input to Bluetooth manually.

The apple version of Google maps has an option to "play audio over bt as phone call" and will interrupt the radio but this option is not available in the Android app.